From seasickness to sunburn and surfboarding, a collection of previously unpublished letters and photos by Agatha Christie detailing the year-long round-the-world trip she took in 1922 are set to be published by HarperCollins.

Leaving behind her two-year-old daughter, Christie began her adventure at the end of January as part of a trade mission ahead of the British Empire Expedition in 1924. Travelling to Hawaii, Canada, America, New Zealand, Australia and South Africa, the young author – who had already published two novels – described her adventures in weekly letters to her mother, also taking photos on her portable camera of the places she visited.

These included Cape Town and Honolulu, where Christie learned to surf. "It was occasionally painful as you took a nosedive down into the sand, but on the whole it was an easy sport and great fun," the author wrote in her autobiography, later picking up "a wonderful, skimpy emerald green wool bathing dress, which was the joy of my life, and in which I thought I looked remarkably well!" and managing to stand upright on her surfboard. "Oh, it was heaven!" she wrote in her memoirs. "Nothing like it. Nothing like that rushing through the water at what seemed to you a speed of about two hundred miles an hour; all the way in from the far distant raft, until you arrived, gently slowing down, on the beach, and foundered among the soft flowing waves."

The book, The Grand Tour, will collect the previously unpublished letters and photos along with postcards, newspaper cuttings and memorabilia picked up by Christie on her journey. HarperCollins struck a deal to publish the collection next April with Christie's grandson Mathew Prichard and the Agatha Christie Archive Trust. Prichard, who is editing and introducing the book, called it a "valuable social record of its time" as well as "a nostalgic record of the happy days of [Christie's] first marriage to my grandfather".

"As well as writing books, Agatha Christie was an inveterate traveller, a keen photographer and a voluminous letter writer," he said. "This record of the 1922 British Empire tour charmingly combines all three skills."

Publisher David Brawn promised the "unique" travelogue would show a "new side" to the crime fiction writer, who has sold over a billion copies of her 80 novels and short story collections and 20 plays. He believes the letters will demonstrate how "her appetite for exotic plots and locations for her books began with this eye-opening trip", with her time in South Africa "very clearly the inspiration for the book she wrote immediately afterwards, The Man in the Brown Suit".

"The letters are full of tales of seasickness and sunburn, motor trips and surf boarding, and encounters with welcoming locals and overbearing Colonials," said Brawn.